Process of changing the light sensitiveness of photographic emulsions and intermediate used therein



- sensitizing substances Patented July 6,

UNITED .s'r

res PATENT-OFFICE.

.QAIUEL E. SHEPPARD, OF ROCHESTER,

CQRPORATION 0! NEW YORK.

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11o Drawing.

This invention relates'to processes for changing the light sensitivenessof hotographic emulsions. vention is. to provide a process by means ofwhich photographic emulsions ma be improved as regards theirlight-sensitiveness, without impairing the other properties of theemulsion. Another object ofthe invention is to provide-a process inwhich a potential sensitizer may be incorporated with the materials ofthe emulsion, and then the sensitizer liberated at the desired .time inthe emulsion-making process. Other objects will hereinafter appear.

Inmy prior application 718,410, filed June 6, 1924, for art of lightsensitive photographic materials, I have shown that light may beprepared by suitably extracting certain organic materials. When thesesubstances are incorpo-' rated in photographic emulsions, such as thoseofthe gelatino-silver-halid type, theygreatly ;:.increase thelight-sensitiveness of such emulsions.

I have now. found that such sensitizing materials may be prepared in alatent form in which they do'not have a sensitizin action, and then canbe readily changed rom such form so that they do have the sensitizingaction. I have 7 they stay in their latent form, when incorporated withthe materials of the emulsions, and may be'converted into the activesensitizing form in such emulsions at the desired time.

In the preferred form of my invention the sensitizing substance iscombined with larly in the case of glucosides, by using a an organicgroup or radical which maintains it in its latent stateuntil it isreleased from such group or radical. For instance, a mustard oilsensitizer may be combined in a gluoside, in which form it is latent orinac tive, as regards sensitizing action.

- While the sensitizing substance may be released from the group orradical by different chemical steps, I prefer to do it, particuhydrolyzing enzyme. I shall now describe one form of my invention by wayof illustration, but it will be understood that the invention is notrestricted to the details'thus given, except as indicated in theappended claims. Since mustard oils and their gluco-' -One object of t ein- 'glucosides,

different cells,

further discovered thatv lpplieationflled December 2, 1925. Serial No.72,811.

sides are readily prepared and easily treated, I- shall refer to them byway of example.

Sensitizing mustard oils are contained in combined or latent form invegetable bodies, particularly in the seeds of the plants of the ordercruciferae. They occur usually asthe monosegroup or radical with whichthe oil is combined acting to prevent light-sensitizing action.

While these glueosides can be hydrolyzed in various ways, I have foundit particu-' .larly convenient to hydrolyze them b means of enzymes. Thelatter can be use in the emulsion itself, without adversely afi'ectingthe latter. Moreover suitable enzymes-occur in the same plants as theglucosides only in and can be obtained in suit. able form bysimpletechnique.

I may, for example, crush the seeds of black mustard (Brasswa n/igra)and macerate them in hot'alcohol (pure natured) which is raised to aboiling point and held at this point for some time. The residue isthenextracted with cold water and evaporated down to a relatively smallvolume. This watery extract is then made slightly acid by the additionof tartaric acid. The liquid'is then still further evaporated andextracted with alcohol. The syrup thus obtained is best diluted andneutralized with potassium carbonate in order to prevent decom osition.

T e syrup in this form constitutes a latent sensitizer because itcontains the sensiethyl or detizing substance, namely the allyl mustardI New Your, nssrenon 'ro EASTMAN KODAK comrm, or nocrms'rnn, NEW max, A"

halid emulsion of the kind described in my above cited prior ap ication,it produces no sensitizing efiect. ut at the same t1me 'itproduces noill effects on the other propertles of the emulsion: It can be thusincorporated atany of the stages in the prepara-' tion of the emulsion,even-the preliminary ones, say in the gelatine for instance.

Finally the emulsion, containing the latent sensitizer, can be greatlyspeeded up or sensitized by liberating the combined mustard oil, such asallyl isothiocyanate, which is contained in'it. This liberation can bedone by melting the emulsion, at a temperature preferably under 50 0.,and adding to ment of the sensitizing operation "be carried so far as tocoat the emulsion on it a relatively-small amount of gelatine containingthe enzyme or ferment. Postponemay even its support while it stillcontains the latent sensitizer, and then overcoat the emulsion withgelatine containing the enzyme. The latter diti'uses into the emulsionand liberates the scusitizer, thereby greatly increasing the lightsensitiveness.

The enzyme or ferment may be prepared in any preferred way. I may, forexample, macerate white mustard seeds (Si/mp5s 017m) and extract themwith cold water, the extract being evaporated in a vacuum below 40 C.until a syrup is obtained. It is desirable to keep the temperature belowthat specified, in order to prevent the destruction of the enzyme byheat. Upon adding alcohol to the syrup the enzyme is precipitated out.This alcoholic precipitate keeps its activity for a considerable time,it it is not exposed to too high a temperature or other proteincoagulating agents. Tt may be incorporated in gelatine.-and then themixture utilized to activate the latent sensitiz'er in the emulsion,

as described hereinabove.

\Vhenthe latent sensitizer, such as a glucoside of an isothiocyanat-e,is incorporated in a colloid, such as gelat-ine, before thecolloid ismade into an emulsion, the product constitutes a valuable and convenientinter mediate in the process of making photographic emulsions,particularly silver-halid ones.

The proportion of latent sensitizer can vary: but in the emulsions andin the interniediates it is used in quantities whichwill yield theamounts of active scnsitizcr indicated in my hereinabovc citedapplication. Having thus described my invention, what I claim as new anddesire to secure by Letters Patent is:

1. The process of changing the light-sensitiveness of a photographicemulsion which comprises incorporating in said emulsionan organiccompound in which asensitizing substance is'combined with a group whichrenders it latent, and. thereafter releasing saidsubstance in activeform from said compound.

2. The process of increasing the lightsensltiveness of ac0ll01ds1lver-salt emulsion which comprises incorporating in said emul-'step of incorporating in said emulsion an organic latent sensitizer.

5. In the process of preparing a colloidsilver-halid emulsion the stepsof incor porating with the ingredients of said emulsion a latentsensitizer capable of being activated by an enzyme, and incorporating anenzyme in said emulsion to activate said sen sitizer. 6. In the processof preparing light-sensitive colloid-silvcr-halid emulsions the steps ofincorporating with the ingredients of said emulsions a latent scnsitizercapable of being activated by an enzyme, mixing an enzyme with acolloid, and incorporating said mixture of colloid and enzyme into saidemulsion to activate said sensitizer.

7. As an intermediate in the manufacture of colloid-silver-halidemulsions, a colloid having distributed therein particles ofsilver-halid and a latent organic sensitizer.

3. As an intermediate in the manufacture of gelatino-silver-halidemulsions, gelatine having distributed therein minute particles ofsilver-halid and a sensitizing compound kept in latent term bycombination with an organlc group.

9. An intermediate in the manufacture of gelatinosilver-halid emulsionscomprising gelatine having distributed therein minute particles ofsilver-halid and a latent sensi' tizer comprising a compound from whichmustard oil can be released by means of an enzyme.

Signed at Rochester, New York, this 25th day of November 1925.

SAMUEL E. SHEPPARD.

